This invention relates to novel wave energy converter (WEC) devices which are responsive to waves having relatively short periods and to WEC buoys (systems) employing such devices.
The design of prior art WECs has been focused, primarily, on the development of “heave” (or up and down) wave responsive systems that are most efficient in highly energetic wave climates with high-amplitude, long-period waves (e.g. US Pacific Northwest, Europe, Australia). The expectation was that heave responsive WEC systems would first become economically viable in these locations. However, heave responsive WEC technologies are comparatively inefficient in wave climates with short period waves (e.g. eastern US, Gulf of Mexico, Hawaii, northern and western UK, Japan).
A WEC technology of interest which may be referred to as a mass-on-spring WEC or MOSWEC technology (see U.S. Pat. No. 7,443,046 and U.S. Pat. No. 8,067,849) includes the use of internal weights (“reaction masses”), attached to an outer hull/container with springs, that oscillate as the waves act upon the hull. An advantage of the MOSWEC technology is that all moving parts may be hermetically sealed in a dry-nitrogen environment, improving its survivability in the ocean environment. However, a problem with the MOSWEC technology is the implementation of the springs. They must be “soft” enough to allow the reaction masses to oscillate at a frequency near the predominant wave frequency, yet be stiff enough to maintain the reaction masses near their center of travel. When the reaction masses are very heavy (a thousand kilograms or more), known physical springs which are needed to counteract gravitational forces are not satisfactory. As a result, the MOSWEC technology is presently limited to relatively small power autonomous WEC applications.
There is a need for WEC devices which are efficient and cost effective for waves of short-period and which do not require springs to counteract gravity (as per the prior art) and for systems which incorporate such WEC devices.